Flame- and/or explosion-proof casings

ABSTRACT

A motor drive assembly for use in fuel-dispensing installations comprising a structural base plate, a pair of elongated outwardly projecting bushings integrally mounted within openings in the base plate, a drive motor subassembly mounted on the base plate having an output shaft extending through one of the bushings, and a sheet metal casing of generally tophat configuration enclosing the motor and having a peripheral flange welded to the base plate for enclosing the motor. A motor switch is mounted within the casing, a switch-operating shaft is rotatably mounted in the other bushing for operating the motor switch and an electrical lead cable to the motor extends through a funnellike opening in the casing having an inwardly projecting flange to which the lead cable is bonded.

United States Patent [72] Inventors Ernest Stanley Ashford Nutley. Sussex: Lawrence Dilger, South Croydon, Surrey, England 1211 Appl. No 842,410 [22] Filed Jan. 27, 1969 [45] Patented Feb. 9, 1971 [73] Assignee Veeder Industries Inc.

Hartford, Conn. a corporation of Connecticut [32] Priority Jan. 26, 1968 [33] Great Britain [31 4245/68 [54] FLAME-AND/OR EXPLOSION-PROOF CASINGS 5 Claims, 2 Drawing Figs.

[52] US. Cl 174/52 174/65: 310/88: 220/88 [51] Int. Cl H H05k 5/04 [50] Field of Search l70/50, 52, 52.5, 50.5, 65; 220/88; 310/88 [56] References Cited UNITED STATES PATENTS 2,355,864 8/1944 Hartzell l74/52.5UX

Primary Examiner-Lewis H. Myers Assistant Examiner-D. A. Tone AltorneyBaldwin, Wight & Brown ABSTRACT: A motor drive assembly for use in fueldispensing installations comprising a structural base plate, a pair of elongated outwardly projecting bushings integrally mounted within openings in the base plate, a drive motor subassembly mounted on the base plate having an output shaft extending through one of the bushings, and a sheet metal casing of generally tophat configuration enclosing the motor and having a peripheral flange welded to the base plate for enclosing the motor. A motor switch is mounted within the casing, a switch-operating shaft is rotatably mounted in the other bushing for operating the motor switch and an electrical lead cable to the motor extends through a funnellike opening in the casing having an inwardly projecting flange to which the lead cable is bonded.

1 ,l a l PATENTED FEB 9 I97! 3) 562,405

SHEET 1 OF 2 imam/U" .BY W

PATENTEU FEB 9197;

SHEET 2 [1F 2 FLAME-AND/OR EXPLOSION-PROOF CASINGS This invention relates to flameand explosion-proof casings for electrical equipment. i

When electrical equipment is used in surroundings in which gases or vapors capable of forming explosive mixtures with air are present, it is essential that the equipment should be housed in a casing which will not permit propagation of flame, resulting from ignition of a gas mixture within the casing, to the surrounding atmosphere, even if such ignition is explosive thus tending to disrupt the casing. In the United Kingdom, the requirements for such casings are laid downin British Standard Specification No. 229.

In order to meet the requirements of this specification, casings of the type concerned have had to be made up of heavy guage case or fabricated components assembled round the equipment to be protected and secured together by nuts and bolts passing through heavy flanges. This form of construction has been necessary in order that the joints at the flanges may be made with, and may maintain under explosive conditions, sufficient accuracy for the airgap between the members not to exceed the maximum which will prevent flame propagation through the gap. Construction in lighter guage metal has not been practicable because even though the casing might withstand the required pressures without actual disruption, the joints at the flanges would almost certainly spring open to an unacceptable extent, quite apart from the difficulty of obtaining sufficiently accurate joints in the first place.

The object of the present invention is to provide a much cheaper and more easily manufactured casing which is capable of being constructed so as to fulfill the requirements of BS8229.

There is an increasing tendency for electrical equipment to be manufactured as modules, which are removed from apparatus as a unit and replaced when maintenance is required, the module removed being returned to the manufacturer or to specialized service depot for servicing orfrepairfSince there is no necessity for user as access to the interior of such modules, it becomes possible to eliminate releasable joints in the casing, and we have found that it is possible to comply with the requirements of BS8229 whilst using housings of relatively light guage material provided that releasable joints are eliminated. I

According to the invention a flameand explosion-proof casing enclosing electrical equipment comprises a rigid base plate on which the equipment is mounted'and a monocoque housing of drawn sheet metal metallurgically bonded to the base plate to form a sealed envelop around the equipment capable of sustaining the stresses generated by the application of explosive pressures within the envelope without disruption.

The invention is described further with reference to the accompanying drawings, which show a preferred embodiment of electrical equipment encased according to the invention.

FIG. 1 showing the casing in diametrical cross section; and

FIG. 2 being a section on the line ll-ll in FIG. 1.

It should be understood that the actual nature of the equipment encased is immaterial to the invention, although in the example shown an electric motor 2 is" controlled by a microswitch 4 and drives an output shaft 6 through gearing 8. The entire assembly is mounted on a rigid baseplate 10 by means of bolts 12. The baseplate itself is provided with means (not shown) by which it can be detachably mounted within the apparatus of which the encased equipment forms part: the encased equipment forming a module which isexchanged when service or repair is required.

The casing is completed by a housing 14 of tophat configuration comprising a cylindrical body closed at one end and provided at the other end with an outwardly extending annular figure 16. The housing is pressed from sheet metal, the selection of which is determined by the drawability required, the form of metallurgical bonding (see below) utilized to unite the housing to the base plate, and the strength required, as well as cost considerations; mild steel is probably the most generally satisfactory material and for a housing some 4 to 6 inches in diameter l6l8 guage material is suitable. A cylindrical or domed housing is preferable because of its resistance to bu rsting stresses.

The housing 14 encloses the equipment mounted on the baseplate l0 and is united to the latter around the flange If) by metallurgical bonding. By this term we mean any process for uniting metallic parts which creates a continuous metallic bond between the parts, such as welding, brazing or soldering. When the housing and the baseplate arc of steel, we prefer to use seam or stitch welding, the automated application of this process being facilitated by the annular shape ofthe flange 16. Similarly, when the equipment enclosed is to be serviced, the annular configuration of the flange [6 allows it to be turned off the baseplate using a suitable lathe. whereupon the remainder of the housing 14 may be removed and discarded, a new housing being bonded to the baseplate after servicing of the equipment. Since the housing 14 (together with the at tached parts described below) is of cheap construction. this wastage is quite acceptable.

A pressing forming a second housing 18 is metallurgically bonded over the closed end 20 of the housing 14 so as to form a cable entry chamber 22 and also to reinforce the housing 14. This cable entry chamber is at present required by the provisions of BS5229 but under certain circumstances it is anticipated that it could be dispensed with, particularly in view of the improved form of cable entry permitted by the construction of the invention. Thus the housing 18 is fomicd with a funnel-shaped orifice 24, the walls of which are brazed or otherwise mctallurgically bonded directly to the metallic sheathing or conduit of a cable 26 entering the housing through this orifice. an arrangement permitted by the sheet metal construction of the housing. It is preferred that the cable be of copper-sheathed mineral-insulated type.

The cable is connected within the housing to the terminals of the plug unit 28 of a plug and socket connector, this unit being set in the end 20 of the housing 14. The socket unit 30 of the conductor is mounted on the equipment enclosed by the housing so that when the preassembled combination of the housing 14 and 18 and the plug unit 28 is placed over the equipment prior to bonding the flange 16 to the baseplate 10, the plug unit 28 will engage the socket unit 30. The position of the plug and socket units could of course be reversed if convenient.

With a unit according to the invention, one problem that arises is that of testing, since the sealed construction provides no convenient means for applying an elevated pressure to the interior of the housing or housings. In order to overcome this problem. a shaft 32 which is journaled in the base plate by a bush 34, and which is angularly movable to actuate the switch 4 by means of a cam 36, is formed with flats 38 which provide passage for the pressurized gas used for testing purposes, the flats being slight enough and the bush long enough not to provide passages of sufficient shortness or cross section to permit flame propagation therealong. Variations of this arrangement are possible, in which either the shaft or the journal is formed with flats or grooves providing passages a long and narrow enough to prevent flame propagation. Similarly, any member passing through a bush in the baseplate even if not rotatable could be modified in this manner to provide the necessary passages.

in order that the test pressure may be communicated to the cable entry chamber 22, a very small aperture 40 is formed in the end 20 of the housing 14, this aperture again being small enough to prevent flame propagation therethrough: it should be noted that for purposes of illustration, this aperture has been shown many times its actual size.

We claim:

1. A fiameand explosion-proof motor drive assembly comprising a metal baseplate having an opening therein, a elongated bushing integrally mounted within the baseplate opening and projecting longitudinally beyond at least one of the opposed faces of the baseplate, a drive motor subassembly secured to the baseplate comprising a rotary electrical motor and a motor-driven rotatable output shaft extending through the elongated bushing, the elongated bushing having a sufficient length to prevent flame propagation therethrough between the shaft and bushing, and a sheet metal explosionproof housing having a generally top hat configuration with a peripheral outwardly extending annular flange integrally bonded to the base plate, the metal baseplate having a heavier gauge than the sheet metal explosion-proof housing and providing a structural support for the drive motor subassembly, and the base plate and sheet metal housing together forming a sealed envelope around the electrical motor resistant to stresses generated by theapplication of explosive pressures within the envelope.

2. A motor drive assembly according to claim 1 wherein the baseplate has a second opening and wherein the motor drive assembly further comprises a second elongated bushing integrally mounted within said second base plate opening and projecting longitudinally beyond at least one of the opposed faces of the baseplate a control shaft extending through the second bushing, a motor switch mounted within the explosionproof sheet metal housing, and switch operating means on the inner end of the control shaft for operating the switch by operation of the control shaft to selectively energize the and deenergize the electrical motor with the control shaft, the second bushing being of sufficient length to prevent flame propagation therethrough between the control shaft and second bushing.

3. A motor drive assembly according to claim 1 wherein the sheet metal housing has a funnellike openingwith a projecting flange and further comprising an electrical lead cable connected to the motor and extending through the funnel opening and integrally bonded to the projecting flange.

4. A motor drive assembly according to claim 3 wherein said flange projects into the housing. i i

5. A motor drive assembly according to claim I wherein the sheet metal explosion proof housing comprises a first housing portion having a generally tophat configuration with a generally cylindrical part an outer end wall and said peripheral outwardly extending annular flange integrally bonded to the bascplate and forming a first chamberrecciving the electrical motor and a second cap housing portion having a generally cylindrical part integrally bonded to said cylindrical part of the first housing portion in partial overlapping rela' tionship therewith to form a second chamber, the end wall of the first housing portion having an opening therein and the drive motor assembly comprising an electrical motor connector received within the end wall opening and having electrical connectors in said second chamber. the cap housing portion having a cable opening. a cable extending through the cable opening and connected to the electrical connectors, and means securing the cable within the cable opening of the cap housing portion resistant to stresses generated by the p application of explosive pressures within the envelope. 

1. A flame- and explosion-proof motor drive assembly comprising a metal baseplate having an opening therein, a elongated bushing integrally mounted within the baseplate opening and projecting longitudinally beyond at least one of the opposed faces of the baseplate, a drive motor subassembly secured to the baseplate comprising a rotary electrical motor and a motor-driven rotatable output shaft extending through the elongated bushing, the elongated bushing having a sufficient length to prevent flame propagation therethrough between the shaft and bushing, and a sheet metal explosion-proof housing having a generally top hat configuration with a peripheral outwardly extending annular flange integrally bonded to the base plate, the metal baseplate having a heavier gauge than the sheet metal explosion-proof housing and providing a structural support for the drive motor subassembly, and the base plate and sheet metal housing together forming a sealed envelope around the electrical motor resistant to stresses generated by the application of explosive pressures within the envelope.
 2. A motor drive assembly according to claim 1 wherein the baseplate has a second opening and wherein the motor drive assembly further comprises a second elongated bushing integrally mounted within said second base plate opening and projecting longitudinally beyond at least one of the opposed faces of the baseplate a control shaft extending through the second bushing, a motor switch mounted within the explosion-proof sheet metal housing, and switch operating means on the inner end of the control shaft for operating the switch by operation of the control shaft to selectively energize the and deenergize the electrical motor with the control shaft, the second bushing being of sufficient length to prevent flame propagation therethrough between the control shaft and second bushing.
 3. A motor drive assembly according to claim 1 wherein the sheet metal housing has a funnellike opening with a projecting flange, and further comprising an electrical lead cable connected to the motor and extending through the funnel opening and integrally bonded to the projecting flange.
 4. A motor drive assembly according to claim 3 wherein said flange projects into the housing.
 5. A motor drive assembly according to claim 1 wherein the sheet metal explosion-proof housing comprises a first housing portion having a generally tophat configuration with a generally cylindrical part, an outer end wall and saiD peripheral outwardly extending annular flange integrally bonded to the baseplate and forming a first chamber receiving the electrical motor, and a second cap housing portion having a generally cylindrical part integrally bonded to said cylindrical part of the first housing portion in partial overlapping relationship therewith to form a second chamber, the end wall of the first housing portion having an opening therein and the drive motor assembly comprising an electrical motor connector received within the end wall opening and having electrical connectors in said second chamber, the cap housing portion having a cable opening, a cable extending through the cable opening and connected to the electrical connectors, and means securing the cable within the cable opening of the cap housing portion resistant to stresses generated by the p application of explosive pressures within the envelope. 